EP-A 2410004 discloses a method to produce a transparent antistatic multilayer stack using polyurethane coatings and conductive materials like Indium Tin Oxide (ITO).
DE-A 102008054981 discloses radiation curable polyurethane coating compositions for wood paper, textile leather etc., unlike the current invention which discloses a composition and method to produce a free polyurethane film with desirable properties.
Similarly, U.S. Pat. No. 5,939,188 discloses transparent protective coatings for improving the environmental durability and not a free polyurethane film with desirable mechanical, thermal and optical properties.
Polymeric films have been an indispensable part in flexible electronic devices. They can be part of the displays or part of the touch panels. Desirably, the films exhibit a combination of properties such as flexibility, transparency, color neutrality and resistivity against heat, light and physical and/or chemical stress. Most of these films used are thermoplastic and are manufactured by either melt extrusion or solution casting, depending on their glass transition temperatures (Tg) or melting temperatures (Tm), and thermal stabilities of the polymeric materials. For low glass transition or melting temperature polymers, melt extrusion is the preferred process due to low production cost. For high Tg (Tm) polymers, melt extrusion will result in optical issues in the films because of gel formation at high temperature extrusion process. In addition, melt extruded films often exhibit high optical retardation. Solvent casting is the process used for those materials that melt extrusion is not possible. The cost of solvent casting method is generally higher than the extrusion method. Main transparent plastic films used for electronic industries include polyesters, polycarbonates and cellulous derivatives. All these films have a relatively low glass transition temperature and generally need a coating to improve their chemical resistance. Moreover, a low glass transition temperature limits the scope of application because of the thermal stress included in the coating processes of conductive layers on these films.